Protein kinases are enzymes that serve as key components of signal transduction pathways by catalyzing the transfer of the terminal phosphate from adenosine 5′-triphosphate (ATP) to the hydroxy group of tyrosine, serine and threonine residues of proteins. As a consequence, protein kinase inhibitors and substrates are valuable tools for assessing the physiological consequences of protein kinase activation. The over-expression or inappropriate expression of normal or mutant protein kinases in mammals has been demonstrated to play significant roles in the development of many diseases, including cancer and diabetes.
Protein kinases can be divided into two classes: those which preferentially phosphorylate tyrosine residues (protein tyrosine kinases) and those which preferentially phosphorylate serine and/or threonine residues (protein serine/threonine kinases). Protein tyrosine kinases perform diverse functions ranging from stimulation of cell growth and differentiation to arrest of cell proliferation. They can be classified as either receptor protein tyrosine kinases or intracellular protein tyrosine kinases. The receptor protein tyrosine kinases, which possess an extracellular ligand binding domain and an intracellular catalytic domain with intrinsic tyrosine kinase activity, are distributed among 20 subfamilies.
Receptor tyrosine kinases of the epidermal growth factor (“EGF”) family, which includes HER-1, HER-2/neu and HER-3 receptors, contain an extracellular binding domain, a transmembrane domain and an intracellular cytoplasmic catalytic domain. Receptor binding leads to the initiation of multiple intracellular tyrosine kinase dependent phosphorylation processes, which ultimately results in oncogene transcription. Breast, colorectal and prostate cancers have been linked to this family of receptors.
Insulin receptor (“IR”) and insulin-like growth factor I receptor (“IGF-1R”) are structurally and functionally related but exert distinct biological effects. IGF-1R over-expression has been associated with breast cancer.
Platelet derived growth factor (“PDGF”) receptors mediate cellular responses that include proliferation, migration and survival and include PDGFR, the stem cell factor receptor (c-kit) and c-fms. These receptors have been linked to diseases such as atherosclerosis, fibrosis and proliferative vitreoretinopathy.
Fibroblast growth factor (“FGR”) receptors consist of four receptors which are responsible for the production of blood vessels, for limb outgrowth, and for the growth and differentiation of numerous cell types.
Vascular endothelial growth factor (“VEGF”), a potent mitogen of endothelial cells, is produced in elevated amounts by many tumors, including ovarian carcinomas. The known receptors for VEGF are designated as VEGFR-1 (Flt-1), VEGFR-2 (KDR), VEGFR-3 (Flt-4). A related group of receptors, tie-1 and tie-2 kinases, have been identified in vascular endothelium and hematopoietic cells. VEGF receptors have been linked to vasculogenesis and angiogenesis.
Intracellular protein tyrosine kinases are also known as non-receptor protein tyrosine kinases. Over 24 such kinases have been identified and have been classified into 11 subfamilies. The serine/threonine protein kinases, like the cellular protein tyrosine kinases, are predominantly intracellular.
Diabetes, angiogenesis, psoriasis, restenosis, ocular diseases, schizophrenia, rheumatoid arthritis, cardiovascular disease and cancer are exemplary of pathogenic conditions that have been linked with abnormal protein tyrosine kinase activity. Thus, a need exists for selective and potent small-molecule protein tyrosine kinase inhibitors.
Illig, C., et al., in US Patent Publication US2009/0105296 A1, published Apr. 23, 2009 discloses c-fms kinase inhibitors of the following structural formula
and pharmaceutically acceptable salts thereof; and a process for their preparation. Illig, C., et al., in Scheme 1, teach preparation of the derivatives of the above structural formula comprising reacting a compound of formula 1-5
with a heterocyclic acid P1—WCOOH (or a corresponding salt thereof P1—WCOOM2, where M2 is Li, Na or K) where P1 is an optional protecting group (for example 2-(trimethylsilyl)ethoxymethyl (SEM) such as when W is imidazole, triazole, pyrrole, or benzimidazole). The coupling can be carried out according to standard procedures for amide bond formation or by reaction with acid chlorides P1—WCOCl or activated esters P1—WCO2Rq (where Rq is a leaving group such as pentafluorophenyl or N-succinimide).
There remains a need for a process for the preparation of compounds of formula (I), wherein the said process is suitable for large scale manufacture.